What? Why?

Fix cBioPortal/cbioportal#6882.

Changes proposed in this pull request:

Zoom + Trim
- Issue: when trimming the timeline, zooming would zoom on the wrong region
- Root cause: start and end of zoom region were determined according to untrimmed timeline. This was happening inside the d3 library itself
- Fix: take the point the the brush generates, determine its placement on the untrimmed timeline, find the nearest tick on the trimmed timeline, replace the point with that.
Cut off circles
- Issue: mousing over points on the bottom lane of the timeline caused them to be cut off when they expanded.
- Fix: added 3 pixels to the height of the svg

Any screenshots or GIFs?

If this is a new visual feature please add a before/after screenshot or gif here with e.g. GifGrabber. zoom